Compound Interest Calculator
See how an initial amount plus regular monthly contributions grows over time when interest compounds. The chart of principal versus interest shows exactly when compounding starts to do the heavy lifting.
Adjust the interest rate, time horizon, and how often interest compounds (annually, quarterly, monthly, or daily) to compare scenarios and understand the true power of starting early.
Projected future value
$325,159
- Total contributions
- $82,000
- Total interest earned
- $243,159
Year-by-year growth
| Year | Contributed (total) | Interest (total) | Balance |
|---|---|---|---|
| 1 | $12,400 | $801 | $13,201 |
| 2 | $14,800 | $1,834 | $16,634 |
| 3 | $17,200 | $3,115 | $20,315 |
| 4 | $19,600 | $4,662 | $24,262 |
| 5 | $22,000 | $6,495 | $28,495 |
| 6 | $24,400 | $8,633 | $33,033 |
| 7 | $26,800 | $11,100 | $37,900 |
| 8 | $29,200 | $13,918 | $43,118 |
| 9 | $31,600 | $17,114 | $48,714 |
| 10 | $34,000 | $20,714 | $54,714 |
| 11 | $36,400 | $24,747 | $61,147 |
| 12 | $38,800 | $29,246 | $68,046 |
| 13 | $41,200 | $34,244 | $75,444 |
| 14 | $43,600 | $39,776 | $83,376 |
| 15 | $46,000 | $45,882 | $91,882 |
| 16 | $48,400 | $52,603 | $101,003 |
| 17 | $50,800 | $59,983 | $110,783 |
| 18 | $53,200 | $68,070 | $121,270 |
| 19 | $55,600 | $76,915 | $132,515 |
| 20 | $58,000 | $86,573 | $144,573 |
| 21 | $60,400 | $97,102 | $157,502 |
| 22 | $62,800 | $108,567 | $171,367 |
| 23 | $65,200 | $121,033 | $186,233 |
| 24 | $67,600 | $134,575 | $202,175 |
| 25 | $70,000 | $149,269 | $219,269 |
| 26 | $72,400 | $165,198 | $237,598 |
| 27 | $74,800 | $182,452 | $257,252 |
| 28 | $77,200 | $201,128 | $278,328 |
| 29 | $79,600 | $221,327 | $300,927 |
| 30 | $82,000 | $243,159 | $325,159 |
Calculation Formulas
P is the starting principal, r is the annual rate (as a decimal), n is the number of times interest compounds per year, and t is the number of years.
Example:
$10,000 at 7% compounded monthly for 30 years → A = 10,000 × (1 + 0.07/12)^(12×30) ≈ $81,165.
This calculator simulates each month, applying an equivalent monthly growth factor f consistent with your compounding frequency, then adding your monthly contribution — so the timing of deposits is exact.
Everything above what you actually put in (starting principal plus all contributions) is compound growth.
Key Figures
| Figure | Value | Description |
|---|---|---|
| Compounding options | Annual → Daily | More frequent compounding earns slightly more at the same nominal rate. |
| Rule of 72 | 72 ÷ rate ≈ years to double | A quick estimate: at 8%, money roughly doubles every 9 years. |
Note: Results are estimates for planning purposes. Rates, fees, taxes, and insurance vary by lender and location — confirm exact figures with a licensed professional before making financial decisions.
Standards & Sources
Last verified: July 2026
- Future value of an annuity (time value of money)
Standard financial mathematics for valuing a stream of equal periodic payments plus an initial sum — the basis of every savings and investment growth projection.
- APY vs. nominal rate (Truth in Savings Act)
Annual Percentage Yield reflects the effect of compounding on a nominal rate. Growth projections here assume the rate you enter is the nominal annual rate compounded at your chosen frequency.
How to Use This Calculator
- Enter your starting amount (initial principal) and any recurring monthly contribution.
- Enter the annual interest rate you expect and the number of years to grow.
- Choose how often interest compounds — monthly is a common default for savings accounts.
- Read your projected future value, total contributions, and total interest earned, then review the year-by-year growth table.
Frequently Asked Questions
What is compound interest?
Compound interest is interest earned on both your original principal and on the interest already added to the balance. Because each period’s interest earns interest in future periods, the balance grows faster over time — the effect accelerates the longer you leave it invested.
How does compounding frequency affect growth?
The more often interest compounds — daily versus monthly versus annually — the more you earn at the same nominal rate, because interest is added to the balance sooner and starts earning on itself. The difference is small over short periods and grows with time and rate.
What is the formula for compound interest?
For a lump sum with no contributions: A = P(1 + r/n)^(n·t), where P is the principal, r is the annual rate (as a decimal), n is compounds per year, and t is years. This calculator extends that by adding your recurring monthly contributions period by period.
Why does starting early matter so much?
Because growth compounds, money invested earlier has more periods to earn interest on interest. Two people contributing the same amount can end with very different balances if one starts a decade sooner — try shifting the number of years here to see the gap.
Related Calculators
CAGR Calculator
Calculate the compound annual growth rate (CAGR) of an investment from its beginning value, ending value, and the number of years.
ROI Calculator
Calculate return on investment (ROI). Enter what you invested and what it is worth to see your net profit, ROI percentage, and annualized return.
Savings Goal Calculator
Find out how much to save each month to reach a goal by your target date, given a starting balance and interest rate. Includes a year-by-year projection.